1. FIELD OF THE INVENTION
The present invention relates to an ignition timing control apparatus for an internal combustion engine for controlling a knocking in the engine.
2. DISCUSSION OF BACKGOUND
FIG. 10 is a block diagram showing a conventional ignition timing control apparatus for an internal combustion engine.
In FIG. 10, a reference numeral 1 designates an acceleration sensor attached to the internal combustion engine to detect a vibration acceleration in the engine, a numeral 2 designates a frequency filter which passes only a frequency signal component having a high sensitivity to a knocking among output singals from the acceleration sensor 1, a numeral 3 designates an analog gate for blocking noises which disturb the detection of the knocking signal in output signals from the frequency filter 2, a numeral 4 designates a gate timing controller 4 for generating an instruction signal to open or close the analog gate 3 in response to the generation of noises, a numeral 5 designates a noise level detector for detecting the level of mechanical vibration noises of the engine except for the knocking signals, a numeral 6 designates a comparator for comparing the output voltage of the analog gate 3 with the output voltage of the noise level detector 5 to produce a knocking detection pulse signal, a numeral 7 designates an integrator which integrates the pulse signal from the comparator 6 to thereby produce an integrated voltage in response to the magnitude of the knocking, a numeral 8 designates a phase shifter for displacing the phase of a reference ignition signal in response to the output voltage of the integrator 7, a numeral 9 designates a rotation signal generator for generating an ignition signal in accordance with a predetermined ignition advance angle characteristic, a numeral 10 designates a waveform shaping circuit which is adapted to shape the ignition signal of the rotation signal generator 9 and at the same time, to control the closing angle in current conduction in an ignition coil 12, and a numeral 11 designates a switching circuit for interrupting or continuing the current conduction to the ignition coil 12 in response to the output signal of the phase shifter 8.
FIG. 11 shows frequency characteristic in the output signal from the acceleration sensor 1. In FIG. 11, a curve A designates the characteristic in a case where a knocking does not take place, and a curve B designates the characteristic in a case where the knocking takes place.
In the output signal of the acceleration sensor 1, there are included a knocking signal, and the other signals generated when the knocking takes place, such as mechanical noises of the engine other than the knocking signal, and various noise components carried on a signal transmission line such as ignition noises, and so on.
In comparing the curve A with the curve B in FIG. 11, it is understood that the knocking signal has a peculiar frequency characteristic. Although the distribution in frequency varies depending on engines to be used and the position of the acceleration sensor 1 attached to the engine, there is clear difference between the case that the knocking occurs and the case that knocking does not occur. Accordingly, by filtering a frequency component of the knocking signal, the noises having the other frequency components are suppressed and the knocking signal can be effectively detected.
FIGS. 12 and 13 show operating waveforms for various elements shown in FIG. 12. FIG. 12 shows mode where there takes place no knocking in the engine, and FIG. 13 shows mode where there take place knockings in the engine.
The operations of the ignition timing control apparatus will be described with reference to FIGS. 12 and 13.
When the internal combustion engine is actuated, the rotation signal generator 9 generates an ignition signal in response to an ignition timing characteristic which is previously determined. The ignition signal is then subjected to waveform-shaping to be transformed into an opening and closing pulse signal with a given closing angle by the waveform shaping circuit 10. The shaped ignition signal drives the switching circuit 11 through the phase shifter 8 to thereby turn on and off current-feeding to the ignition coil 12. When the current is interrupted, the engine is fired by an ignition voltage produced in the ignition coil 12. Vibrations in the engine caused in the operation of the engine are detected by the acceleration sensor 1.
When there is no knocking in the engine, the vibrations in the engine resulted from the knocking do not occur. However, the mechanical noises and the ignition noises are carried on the signal transmission line even in the ignition F, and they are contained in the output signal of the acceleration sensor 1 as shown in FIG. 12a. When the output signal is passed through the frequency filter 2, the machanical noise components are fairly suppressed as shown in FIG. 12b. However, the output signal having a large ignition noise component is sometimes outputted even after being passed through the frequency filter 2 since the magnitude of the ignition noise component is large. In this case, the ignition noises are recognized as knocking signals. Therefore, the analog gate 3 is used to block the ignition noises by closing its gate during a certain period when the ignition takes place, this being effected by the output of the gate timing controller 4 which is triggered by the output of the phase shifter 8 (FIG. 12c). As a result, only mechanical noises having a low level as indicated by A in FIG. 12d remains in the output of the analog gate 3.
On the other hand, the noise level detector 5 responds to change of the peak value of the output signal of the analog gate 3. In this case, the noise level detector 5 has the characteristics capable of responding to a relatively slow change in the peak value of mechanical noises and generates a d.c. voltage slightly higher than the peak value of the mechanical noises (as indicated by B in FIG. 12d).
Accordingly, since the output of the noise level detector 5 is greater than the average peak value of the output signal from the analog gate 3 as shown in FIG. 12d, no output signal is produced from the comparator 6 for comparing both signals as shown in FIG. 12e, with the result that the noise signal is completely removed. Accordingly, since there is no output voltage from the integrator 7 as shown in FIG. 12f, a phase angle (difference of phase between the input and output signals of the phase shifter in FIGS. 12g and 12h) given by the phase shifter 8 is also zero. Accordingly, the phase of opening and closing the switching circuit driven by the output signal of the phase shifter 8, i.e. the phase of the current intermittently produced in the ignition coil 12 is the same as the phase of the reference ignition signal as the output from the waveform shaping circuit 10, whereby the ignition timing corresponds to the reference ignition timing.
When a knocking takes place, the output of the acceleration sensor 1 contains the knocking signal with a certain time delay from the ignition timing as shown in FIG. 13a, and the signal after being passed through the frequency filter 2 and the analog gate 3 is such that the knocking signal is overlapped with the mechanical noises as indicated by A in FIG. 13d. Of the signal passed through the analog gate 3, since the rising part of the knocking signal is steep, response of the output voltage of the noise level detector 5 to the knocking signal is delayed. As a result, the input signals to the comparator 6 respectively take the form as shown by A and B in FIG. 13d, whereby a pulse signal is produced in the output of the comparator 6 as shown in FIG. 13e.
The integerator 7 integrates the pulses to thereby produce an integrated voltage as shown in FIG. 13f. Since the phase shifter 8 displaces the output signal (the reference ignition signal as by FIG. 13g) of the waveform shaping circuit 10 to the side of delay in time in response to the output voltage of the integrator 7, the phase of the output signal of the phase shifter 8 is lagged with respect to the phase of the reference ignition signal of the waveform shaping circuit 10. With such lag in phase of the output of the phase shifter 8, the switching circuit 11 is actuated with the phase as shown in FIG. 13h. Accordingly, there causes delay in ignition timing, whereby the knocking is suppressed. Thus, the optimum ignition timing controlling is obtained in a manner as described with reference to FIGS. 12 and 13.
In the conventional apparatus having the above-mentioned construction, a reducing rate (a speed for shifting ignition timing toward the advance angle side with respect to the reference) in the output of the integrator 7 has a large time constant of a second or seconds per one revolution angle of the engine. The reducing rate suppress occurrence of a large knocking which may take place when a speed for shifting the igntion timing toward the advance angle side is too fast whereby the ignition timing falls rapidly in a knocking region. Thus, the reducing rate is an important factor to control the ignition timing. Accordingly, in order to obtain an amount of knocking at each time of the detection of the knocking from the outputs of the integrator 7, it is necessary to obtain the output of the integrator 7 at the time just before and just after the detection of the knocking and the difference between the values detected before and after the detection of the knocking, i.e. an amount of change of output from the integrator 7 at each time of the detection of the knocking. This requires complicated operations. The difference in outputs or the change of an output can not be obtained by taking only the value of the integrator 7 at the time of the detection of knocking. Accordingly, it is required, for instance, such a operation that the output of the integrator 7 before the generation of a knocking is memorized, and when the knocking takes place, the ouptut of the integrator 7 just before the generation of knocking is compared with the output just after the generation of knocking to thereby obtain the value of difference.
On the other hand, there is an increasing tendency of finely controlling the engine of an automobile, namely, a fine control is made for each cylinder to realize a good condition of combustion for all of the cylinders whereby the performance of the engine is increased. As one way to perform the fine control of the engine, it is necessary to detect the magnitude of the knocking at each time of the generation of it and to obtain the magnitude of the knocking for each of the cylinders. However, complicated operations were required to obtain the magnitude of the knocking at each time of the generation of the knocking from the output of the integrator 7 in the conventional apparatus. Further a large sized circuit was required for the above-mentioned purpose.